This invention relates to electronic circuits and more particularly to electronic power switching circuits which include a heatsink.
Power hybrid circuits commonly include silicon power switching devices, such as MOSFETs, mounted on electrically insulating ceramic members disposed on a metallic heatsink, such as copper. The sandwich of silicon, ceramic and copper are joined into a sandwich by soldering, after which the electrical connections are made in any suitable manner, such as by wire bonding, which comprises ultrasonically welding aluminum wire to the silicon device and to a current-carrying electrode, for example. The joining of heat spreaders, ceramic insulators and silicon devices place the various electric terminals at different elevations, thereby requiring relatively long wire bonds which adversely affects performance and reliability. To avoid these adverse effects, prior art heatsinks were fabricated by soldering or braising various sized blocks and plates to a base member to achieve uniform wire bond lengths, to vary the mass of the article and to support the required silicon devices.
One application for power hybrid circuits of the type described is in a dual storage battery for automotive and similar uses. Such batteries include a primary cell unit which is used for normal operation and an auxiliary or reserve cell unit which is normally on standby. Should the primary unit become discharged, the auxiliary unit is switched into the vehicle's electrical circuity. This permits the vehicle to be started so that the primary unit can be recharged, after which the primary unit is switched into the circuit and the auxiliary unit returned to its reserve status. This application requires that the electronics switching devices carry momentarily high currents, such as, for example, in the order of several hundred amps or more. As a result, a substantial heatsink is required.